Rebellion had been planning to bring back its second R-13 for the first time since last September's Silverstone opener, with Romain Dumas, Louis Deletraz and Nathanael Berthon set to share driving duties as preparation for the Le Mans 24 Hours in September.
However, an entry list for the Spa race on August 15 reveals that the Swiss team will be fielding only its full-season #1 entry for Bruno Senna, Gustavo Menezes and Norman Nato.
Ginetta meanwhile is missing its second WEC race in succession, having also been absent for the previous race at Austin back in February, before the 2019/20 season was put on hold by the global coronavirus pandemic.
Last week's updated Le Mans entry list featured just one entry from the British marque, with Mike Simpson the only confirmed driver aboard the #6 G60-LT-P1.
With the entry being bolstered by the return of the ByKolles ENSO CLM P1/01, it means four cars will take part in LMP1, including both Toyota TS050 Hybrids - one more than at Austin, which featured a record-low entry for the top class.
The LMP2 division meanwhile will feature 10 cars, with the full-season contingent of eight cars joined by Eurasia Motorsport's Ligier JS P217 and an extra Goodyear-shod Oreca 07 entered by European Le Mans Series regular squad Algarve Pro Racing.
American gentleman driver John Falb is the sole driver listed for the Algarve Pro car, while Nobuya Yamanaka and Daniel Gaunt are slated to drive the Eurasia Ligier, although they will not be joined by SUPER GT and Super Formula ace Nick Cassidy as first planned.
High Class Racing is also shown as being back on Goodyear tyres having switched to the Michelin camp for the previous race at Austin.
Despite previous doubts over Toyota protege Kenta Yamashita's availability for the Spa race, the Japanese driver is listed as part of the Danish team's driver line-up.
Both the GTE Pro and GTE Am classes have their usual number of cars - six and 11 respectively - to make for a total field of 31 cars.